I-v converting module

ABSTRACT

An I-V converting module includes: a current output sensor, an I-V transforming circuit, a sampling and holding circuit, a source follower, a loop switch, and a bypass circuit. A drain of the source follower is connected to an input/output end of the sampling and holding circuit. A source of the source follower is connected to an input end of the I-V transforming circuit and an output end of the current output sensor, and a gate of the source follower is connected to an output end of the I-V transforming circuit via the loop switch, and to the bypass circuit. When the loop switch is closed and the bypass circuit is disabled, a feedback loop formed by the source follower, the I-V transforming circuit and the loop switch is conducted, and the I-V converting module enters into a sampling setup stage.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of international applicationNo. PCT/CN2016/095429 filed on Aug. 16, 2016, which is herebyincorporated by reference herein, in its entirety.

TECHNICAL FIELD

The present disclosure relates to the field of electronic circuittechnologies, and in particular, to an I-V converting module.

BACKGROUND

An existing current to voltage converting module, i.e. an I-V convertingmodule, as shown in FIG. 1, consists of a regular I-V transformingcircuit 1, a sampling and holding circuit 2, and a current output sensor3. The sampling and holding circuit 2 counteracts a direct currentcomponent output by the current output sensor 3 to enlarge an outputdynamic range of the I-V converting module. However, a setup speed ofthe existing sampling and holding circuit 2 is relatively slow. Thisdecreases a speed of the entire I-V conversion, in other words, thisresults in a longer time for obtaining an alternating current signal.

In the existing I-V converting module, if a current output by thecurrent output sensor 3 is I₀, and the direct current component outputby the current output sensor 3 is I, in a sampling setup stage, that is,when a control signal sh is at a high level, a switch S₂ is closed. Inthis situation, a P-type field-effect transistor M₂ is equivalent to aresistor having a resistance of gm. Because a field-effect transistor M₂usually works in a sub-threshold region, the resistance of thefield-effect transistor M₂ is in positive proportion to the directcurrent component I output by the current output sensor 3, that is,gm=α·I (αis a constant). When the control signal sh is at a low level,that is, a moment when the switch S₂ is closed, a voltage of a plate ofa parasitic capacitor C₃ connected to a sampling capacitor C₂ begins tobe established, and a time constant of the sampling and holding circuit2 is therefore τ=(C₃+C₂)/gm=(C₃+C₂)/α·I.

Taking a parameter that frequently appears in the above formula as anexample, if gm=α·I=1 μS, C₃=100 pF, and C₂ =1 pF, the time constant isτ≈100 μs. During the conception of the present invention, the inventordiscover that the existing technology has the following problems: thesetup speed of the sampling and holding circuit 2 is very low, andconsequently the I-V transforming circuit 1 needs a long time to collectan alternating current component output by the current output sensor 3and the converting rate of the I-V converting module may be severelydecreased.

SUMMARY

Some embodiments of the present disclosure aim to provide an I-Vconverting module, to greatly accelerate a setup speed of a sampling andholding circuit, thereby increasing the converting rate of the I-Vtransforming circuit.

To solve the above technical problem, some embodiments of the presentdisclosure provide an I-V converting module including: a current outputsensor, an I-V transforming circuit, a sampling and holding circuit, asource follower, a loop switch and a bypass circuit. A drain of thesource follower connects to an input/output end of the sampling andholding circuit, a source of the source follower connects to an inputend of the I-V transforming circuit and an output end of the currentoutput sensor, and a gate of the source follower connects to an outputend of the I-V transforming circuit via the loop switch; and the gate ofthe source follower further connects to the bypass circuit. When theloop switch is closed and the bypass circuit is disabled, a feedbackloop that is formed by the source follower, the I-V transforming circuitand the loop switch is conducted, and the I-V converting module entersinto a sampling setup stage. When the loop switch is disconnected andthe bypass circuit is enabled, the feedback loop is bypassed, and theI-V converting module enters into an I-V converting stage.

Compared with existing technologies, some embodiments of the presentdisclosure provide an I-V converting module. In a sampling setup stage,a feedback loop formed by the source follower, the I-V transformingcircuit and the loop switch, is conducted, and the source followerseparates the sampling and holding circuit from the current outputsensor, so that a time constant formed by the sampling and holdingcircuit and the current output sensor greatly decreases, the setup speedof the sampling and holding circuit is greatly accelerated, and theconverting rate of the I-V converting module is increased. Moreover, inthe present disclosure, a voltage of an output end of the current outputsensor in the sampling setup stage maintains to be unchanged, whichensures that an output current does not to change with a voltage of theoutput end, and which ensures the consistency of the magnitude of anoutput current of the current output sensor.

In addition, the I-V converting module further includes a loopcapacitor. The loop capacitor is connected between the gate of thesource follower and the input end of the I-V transforming circuit toimprove the stability of the feedback loop.

In addition, the bypass circuit includes a bypass switch and a powersupply, and the bypass switch is connected between the gate of thesource follower and the power supply, wherein the bypass circuit isdisabled when the bypass switch is disconnected. This embodimentprovides a specific example of a bypass circuit, and this bypass circuitis relatively simple.

In addition, the bypass circuit includes a first bypass switch, a secondbypass switch, and a ground plane. The first bypass switch connectsbetween the gate of the source follower and the ground plane. The secondbypass switch connects between the source and the drain of the sourcefollower. Wherein the bypass circuit is disabled when both of the firstbypass switch and the second bypass switch are disconnected. Thisembodiment provides another specific implementation manner of anotherbypass circuit. Compared with the above bypass circuit, a ripple in thepower supply is avoided to be introduced to the I-V transformingcircuit, thereby increasing the signal-to-noise ratio of an I-Vtransforming circuit 1, that is, improving the power supply rejectioncapability of the I-V transforming circuit.

In addition, an inverting amplifier includes an inverter or anoperational amplifier. Two different types of inverting amplifiers areprovided to expand an application scenario of the present disclosure.

In addition, a transforming path includes a resistor and a switch thatare connected in series, or a capacitor and a switch that are connectedin series. Two different types of transforming paths are provided toensure the feasibility of the present disclosure.

In addition, the source follower includes an N-type field-effecttransistor or an NPN-type triode. Different types of source followersare provided to expand an application scenario of the presentdisclosure.

In addition, the loop switch is an electronic switch or a physicalswitch. Different types of loop switches are provided to expand anapplication scenario of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit structural diagram of an existing I-V convertingmodule in the background;

FIG. 2 is a circuit structural diagram of an I-V converting moduleaccording to a first embodiment of the present disclosure;

FIG. 3 is a circuit structural diagram of an I-V transforming circuit ofa first example according to the first embodiment;

FIG. 4 is a circuit structural diagram of an I-V transforming circuit ofa second example according to the first embodiment;

FIG. 5 is a circuit structural diagram of an I-V converting moduleaccording to a second embodiment; and

FIG. 6 is a circuit structural diagram of an I-V converting moduleaccording to a third embodiment.

DETAILED DESCRIPTION

In order to make the objectives, technical solutions and advantages ofthe present disclosure clearer, some of embodiments of the presentdisclosure will be further described in details with reference to thedrawings. However it should be understood by the person skilled in theart that in some embodiments of this patent application, varioustechnical details are described to make this application easier to beunderstood. However, the technical solutions sought to be protected bythe claims of this patent application may be implemented even withoutthe technical details and the various changes and modification made tothe embodiments below.

A first embodiment of the present disclosure relates to an I-Vconverting module, i.e., a current to voltage converting module. Asshown in FIG. 2, the I-V converting module includes: an I-V transformingcircuit 1, a sampling and holding circuit 2, a current output sensor 3,a source follower M₁, a loop switch S₁, and a bypass circuit.

The source follower M1 includes an N-type field-effect transistor or anNPN-type triode, but without any limitation; and as an example, thisembodiment is described by using the N-type field-effect transistor.

In this embodiment, a drain of the source follower M₁ connects to aninput/output end of the sampling and holding circuit 2, a source of thesource follower connects to an input end V_(in) of the I-V transformingcircuit 1 and an output end of the current output sensor 3, a gate ofthe source follower connects to an output end V_(out) of the I-Vtransforming circuit 1 via the loop switch S₁, and the gate of thesource follower also connects to the bypass circuit.

The loop switch S₁ is an electronic switch or a physical switch. Forexample, the electronic switch may be a field-effect transistor or abipolar junction transistor. This embodiment has no limitation on thetype of the loop switch S₁.

In this embodiment, the current output sensor 3 includes a parasiticcapacitor C₃. One end of the parasitic capacitor C₃ connects to a groundterminal GND1, and the other end of the parasitic capacitor C₃ connectsto an output end of the current output sensor 3. The output end of thecurrent output sensor 3 connects to the source of the source follower M₁and the input end V_(in) of the I-V transforming circuit 1. A current I₀is output by the output end of the current output sensor 3. A directcurrent component output by the current output sensor 3 is I.

In this embodiment, the sampling and holding circuit 2 includes: asampling field-effect transistor M₂, a sampling capacitor C₂, and asampling switch S₂. One end of the sampling capacitor C₂ and a source ofthe sampling field-effect transistor M2 are connected to a power supplyvoltage VDD. The other end of the sampling capacitor C₂ connects to agate of the sampling field-effect transistor M₂ and one end of thesampling switch S₂. The other end of the sampling switch S₂ and a drainof the sampling field-effect transistor M₂ are connected to the drain ofthe source follower M₁.

In the sampling and holding circuit 2, when the sampling switch S₂ isclosed, the sampling field-effect transistor M₂ is equivalent to aresistor having a resistance of gm. Because the source follower M₁usually works in a sub-threshold region, the resistance of the samplingfield-effect transistor M₂ is in positive proportion to the directcurrent component I output by the current output sensor 3, i.e. gm=α·I(αis a constant).

In this embodiment, the I-V transforming circuit 1 includes an invertingamplifier and at least one transforming path. The transforming pathconnects between an input end and an output end of the invertingamplifier. The input end and the output end of the inverting amplifierrespectively form the input end V_(in) and the output end V_(out) of theI-V transforming circuit 1.

The inverting amplifier includes an inverter or an operational amplifier(but without any limitation). The transforming path includes a resistorand a switch which are connected in series, or a capacitor and a switchwhich are connected in series. Moreover, there may be multiple or asingle transforming path. The type of serial connection of thetransforming path and the number of the transforming paths may bespecifically set according to actual situations in this embodiment, andthis is not limited in this embodiment.

This embodiment provides two examples of the I-V transforming circuit 1,and specific descriptions are as follows.

In an I-V transforming circuit of the first type, as shown in FIG. 3,the inverting amplifier is an inverter 11, and a transforming path 12includes a capacitor C₁₂ and a converting switch S₁₂ which are connectedin series. Specifically, one end of the capacitor C₁₂ connects to aninput end V_(in) of the inverter 11, and the other end of the capacitorC₁₂ connects to one end of the converting switch S₁₂. The other end ofthe converting switch S₁₂ connects to an output end V_(out) of theinverter 11. The input end V_(in) and the output end V_(out) of theinverter 11 respectively form the input end Vin and the output endV_(out) of the I-V transforming circuit 1.

In the I-V transforming circuit of the first type, when the convertingswitch S₁₂ is disconnected, the transforming path 12 does not work. Inthis situation, the I-V transforming circuit 1 is equivalent to anopen-loop amplifier. When the converting switch S₁₂ is closed, the I-Vtransforming circuit 1 converts an input current signal I_(in) into avoltage signal and outputs the voltage signal. The converting switch S₁₂is controlled by a clock signal φ to disconnect and close at intervals.The input current signal I_(in) is an alternating current componentoutput by the current output sensor 3.

In an I-V transforming circuit of the second type, as shown in FIG. 4,the inverting amplifier is an operational amplifier 13, and thetransforming path 12 includes a resistor R₁₂ and a converting switch S₁₂which are connected in series. Specifically, one end of the resistor R₁₂connects to an input end Vin of the operational amplifier 13, that is,an inverting input end of the operational amplifier 13. An in-phaseinput end of the operational amplifier 13 receives a common-mode powersupply V_(cm). The other end of the resistor R12 connects to an end ofthe converting switch S₁₂. The other end of the converting switch S12connects to an output end V_(out) of the operational amplifier 13. Theinput end V_(in) and the output end V_(out) of the operational amplifier13 respectively form the input end V_(in) and the output end V_(out) ofthe I-V transforming circuit 1.

In the I-V transforming circuit 1 of the second type, when theconverting switch S₁₂ is disconnected, the transforming path 12 does notwork. In this situation, the I-V transforming circuit 1 is equivalent toan open-loop amplifier. When the converting switch S₁₂ is closed, theI-V transforming circuit 1 converts an input current signal I_(in) intoa voltage signal and outputs the voltage signal.

In practice, there are various other implementing manners of the I-Vtransforming circuit 1 which are not limited in this embodiment. Anyimplementing manner of the I-V transforming circuit 1 that can make theI-V converting module work normally may be applied to this embodiment.For example, the I-V transforming circuit 1 may be connected by anoperational amplifier and a transforming path including a capacitor anda switch which are connected in series, or may be connected by aninverter and a transforming path including a resistance and a switchwhich are connected in series.

In this embodiment, the bypass circuit may include a bypass switch S₃and a power supply. The bypass switch S₃ connects between a gate of thesource follower M1 and the power supply. The power supply of the bypasscircuit may be the power supply voltage VDD of the sampling and holdingcircuit 2, or may be an individual power supply. This is not limited inthis embodiment.

In the bypass circuit, the bypass circuit is disabled when the bypassswitch S₃ is disconnected, that is, the bypass circuit is in anon-working state. The bypass circuit is enabled when the bypass switchS₃ is closed, that is, the bypass circuit is in a working state. In thiscase, the gate of the source follower M₁ connects to the power supply,the source follower M₁ enters into a linear region, and the sourcefollower M₁ is equivalent to a closed switch.

In this embodiment, when a control signal sh is at a high level, theloop switch S₁ is closed and the bypass circuit is disabled, that is,the bypass switch S₃ is disconnected. A feedback loop, formed by thesource follower M₁, the I-V transforming circuit 1, and the loop switchS₁, is conducted, and the I-V converting module enters into a samplingsetup stage. The loop switch S₁ is disconnected and the bypass circuitis enabled, that is, the bypass switch S₃ is closed, the feedback loopis bypassed, and the I-V converting module enters into an I-V convertingstage.

For example, in the I-V converting module, as shown in FIG. 2 and FIG.3, in this embodiment, the loop switch S₁ and the sampling switch S₂ arecontrolled by the control signal sh, and the converting switch S₁₂ iscontrolled by a control signal sh. When the control signal sh is at ahigh level, the loop switch S₁ and the sampling switch S₂ are closed,and the converting switch S₁₂ and the bypass switch S₃ are disconnected.The feedback loop is conducted, the source follower M₁ enters into asaturation region and separates the sampling and holding circuit 2 fromthe current output sensor 3. The I-V converting module enters into asampling setup stage, that is, the sampling and holding circuit 2 beginsto sample a current, the gate and the drain of the sampling field-effecttransistor M₂ are short-circuited, and charges the sampling capacitorC₂, and finally a voltage V_(c2) in one end of the sampling capacitor C₂stabilizes to a voltage value, making a drain current of the samplingfield-effect transistor M₂ be equal to the direct current component Ioutput by the current output sensor 3. In this case, the samplingfield-effect transistor M₂ is equivalent to a resistor having aresistance of gm, and the resistor, the sampling capacitor C₂, and acapacitor seen from the drain of the source follower M₁ are connected inparallel to generate a time constant τ1. When the control signal sh isat a low level, the loop switch S₁ and the sampling switch S₂ aredisconnected, and the converting switch S12 and the bypass switch S₃ isclosed. The I-V converting module enters into an I-V converting stage,the sampling field-effect transistor M₂ outputs a constant current andcounteracts the direct current component I. At the same time, the sourcefollower M₁ enters into the linear region. In this situation, the sourcefollower M₁ is equivalent to a closed switch, the I-V transformingcircuit converts an alternating-current signal output by the currentoutput sensor 3 into a voltage output signal.

Specifically, in the existing technology, in the sampling setup stage,that is, when the control signal sh is at a high level, the switch S₂ isclosed, and a voltage of a plate of the parasitic capacitor C₃ connectedto the sampling capacitor C₂ begins to be established. In thissituation, the sampling field-effect transistor M₂ is equivalent to aresistor having a resistance of gm. Because the sampling field-effecttransistor M₂ usually works in a sub-threshold region, the resistance ofthe sampling field-effect transistor M₂ is in positive proportion to thedirect current component I output by the current output sensor 3, thatis, gm=α·I , where α is a constant, and a time constant of the samplingand holding circuit 2 is τ=(C₃+C₂)/gm=(C₃+C₂)/α·I.

In this embodiment, because the source follower M₁ is in the saturationregion, the channel thereof is pinched off, it is hard to see acapacitor from the drain of the source follower M₁. Therefore, the timeconstant τ1=C₂/gm1, where gm1 is a transconductance of the samplingfield-effect transistor M₂. Compared with the existing time constantτ=(C₃+C₂)/gm=(C₃+C₂)/α·I, where α is a constant and is a ratio of gm toI, C₃ has no impact on the time constant τ1. If gm₁=1 μs, C₃=100 pF, andC₂=1 pF, the time constant of the sampling and holding circuit 2 is τ≈1μs, that is, compared with an existing sampling and holding circuit, thesetup speed of the sampling and holding circuit 2 is almost increased by100 times (usually is increased by 10 to 100 times). Therefore, the I-Vtransforming circuit 1 only needs a very short time to convert thealternating current component output by the current output sensor 3.

In detail, in the existing technology, in the I-V transforming circuit1, a time constant of the input end Vin is τ2=C₃·Req, where Req is anequivalent impedance of an input end V_(in) in a loop formed by thetransforming path 12 and the inverter 11. Assuming that a gain of theinverter 11 is A, it can be deducted that Req=1/(gm₂·A) ,where gm₂ is atransconductance of the source follower M1, and the time constant of theinput end V_(in) can be changed to τ2=(C₃+A)/A.

In this embodiment, in the I-V transforming circuit 1, the time constantof the input end Vin is τ2=C₃·Req, where Req is an equivalent impedanceof an input end Vin in a loop including the transforming path 12 and theinverter 11. Assuming that a gain of the inverter 11 is A, it can bededucted that Req=1/(gm₂·A), where gm₂ is a transconductance of thesource follower M1, and the time constant of the input end Vin can bechanged to τ2=(C₃+A)/(gm₂·A). Compared with the existing τ2=(C₃+A)/Atechnology, the setup speed of the input end V_(in) may be greatlyincreased by approximately 10 to 100 times.

Compared with the existing technologies, this embodiment provides an I-Vconverting module, the feedback loop is formed by the source followerM1, the I-V transforming circuit 1, and the loop switch S1, enabling thesource follower M1 to be in the saturation region in the sampling setupstage, so as to separate the parasitic capacitor C₃ from the samplingcapacitor C₁, that is, to separate the sampling and holding circuit 2from the current output sensor 3. A time constant formed by theparasitic capacitor C₃ and the sampling capacitor C₁ is greatlydecreased, thereby greatly accelerating the setup speed of the samplingand holding circuit 2, and increasing the converting rate of the I-Vtransforming circuit. A control circuit of the I-V converting moduleprovided by the present invention is relatively simple, and the formedfeedback loop reuses the inverting amplifier in the I-V transformingcircuit, which reduces the circuit costs.

A second embodiment of the present invention relates to an I-Vconverting module. Improvements are made in the second embodiment basedon the first embodiment, and the main improvement is: in the secondembodiment of the present invention, as shown in FIG. 5, a loopcapacitor C₁ is added in the feedback loop.

In this embodiment, the loop capacitor C₁ connects between the gate ofthe source follower M₁ and the input end V_(in) of the I-V transformingcircuit 1. The loop capacitor C₁ is in parallel connection with theinverter 11. Due to the Miller effect, the loop capacitor C₁ is doubledto the source of the source follower M₁. Therefore, the source of thesource follower M₁ generates a low-frequency pole to make the feedbackloop more stable.

For example, in this embodiment, as shown in FIG. 3 and FIG. 5, in theI-V converting module, the time constant of the input end V_(in) of theI-V transforming circuit 1 is τ2=C₃·Req, where Req is an equivalentimpedance of an input end V _(in) in a loop including the transformingpath 12 and the inverter 11. Assuming that a gain of the inverter 11 isA, it can be deducted that Req=1/(gm₂·A), where gm₂ is atransconductance of the source follower M1, and the time constant of theinput end Vin can be changed to τ2=(C₃+C₁·A)/(gm₂·A). Compared withτ2=(C₃+A)/(gm₂·A) in the first embodiment, the setup speed of the inputend V _(in) is greatly increased.

Compared with the technology of the first embodiment, this embodimentadds the loop capacitor C₁ in the feedback loop, thereby improving thestability of the feedback loop.

A third embodiment of the present invention relates to an I-V convertingmodule. The third embodiment is substantially similar to the secondembodiment, and the main difference is: in the second embodiment, thebypass circuit includes the bypass switch and the power supply. However,in the third embodiment of the present invention, as shown in FIG. 6,the bypass circuit includes a first bypass switch S₃ (that is, thebypass switch S₃ in the second embodiment), a second bypass switch S₄,and a ground plane GND2.

In this embodiment, the first bypass switch S₃ connects between the gateof the source follower M₁ and the ground plane GND2; and the secondbypass switch S4 connects between the source and the drain of the sourcefollower M₁.

Preferably, the second bypass switch S₄ uses a P-type field-effecttransistor, but without any limitation on the type of transistor.

In the bypass circuit, when both of the first bypass switch S₃ and thesecond bypass switch S₄ are disconnected, the bypass circuit isdisabled, that is, the bypass circuit is in a non-working state. Whenboth of the first bypass switch S₃ and the second bypass switch S₄ areclosed, the bypass circuit is enabled, that is, the bypass circuit is ina working state.

In this embodiment, when a control signal sh is at a high level, a loopswitch S1 is closed, and the first bypass switch S₃ and the secondbypass switch S4 are disconnected. When the feedback loop is beginningto work, the source follower M1 enters into the saturation region (dueto a negative feedback). When sh is at a low level, the loop switch S₁is disconnected, and both of the first bypass switch S₃ and the secondbypass switch S₄ are closed, and the feedback loop is bypassed. In thiscase, the I-V transforming circuit is equivalent to a regulartransforming circuit, the gate of the source follower M₁ connects to theground plane GND2, and the source follower M1 enters into a cutoffregion. At the same time, the second bypass switch S₄ is closed, and thesource follower M₁ is short-circuited.

Compared with the second embodiment, the mechanism of the bypass circuitin this embodiment is different. In the sampling setup stage of thesecond embodiment, the gate of the source follower M₁ is pulled to aterminal of the power supply. There is usually a relatively big voltageripple at the terminal of the power supply, and there is a parasiticcapacitor between the gate of the source follower M₁ and the source aswell as the drain of the source follower M₁. Therefore, the bypasscircuit may introduce the ripple of the voltage to the I-V transformingcircuit 1, that is, a large amount of noise may be introduced, resultingin impact on a final signal-to-noise ratio. In this embodiment, in thesampling setup stage, the gate of the second bypass switch S₄ (whenbeing a P-type field-effect transistor) is grounded and is conducted theshort-circuited source follower M₁, and the gate of the source followerM₁ connects the ground plane GND2 (that is, is grounded), avoidingintroducing the ripple of the power supply to the I-V transformingcircuit, so as to increase the signal-to-noise ratio of the I-Vtransforming circuit 1, that is, to improve the power supply rejectioncapability of the I-V transforming circuit.

Compared with this embodiment, in the second embodiment, when the sourcefollower is in the linear region in the sampling setup stage, the sourcefollower is equivalent to a closed switch, such that some switches inthe circuit are reduced, and the costs as well, and the controlcomplexity of the I-V converting module is decreased.

It should be noted that, modules involved in this embodiment are alllogical modules. During actual application, a logical unit may be aphysical unit, or may be part of a physical unit, or may be implementedas a combination of multiple physical units. In addition, to highlightthe innovative part of the present invention, units without very closerelationship with the solving of the technical problems in the presentinvention are not introduced in this embodiment, which does not indicatethat other units are not included in this embodiment.

A person of ordinary skill in the art can understand that the aboveembodiments are specific embodiments to implement the present invention,but during actual application, various changes can be made to the formsand details without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. An I-V converting module, comprising: a currentoutput sensor, an I-V transforming circuit, a sampling and holdingcircuit, a source follower, a loop switch, and a bypass circuit; whereina drain of the source follower is connected to an input/output end ofthe sampling and holding circuit, a source of the source follower isconnected to an input end of the I-V transforming circuit and an outputend of the current output sensor, and a gate of the source follower isconnected to an output end of the I-V transforming circuit via the loopswitch; and wherein the gate of the source follower is further connectedto the bypass circuit; wherein when the loop switch is closed and thebypass circuit is disabled, a feedback loop formed by the sourcefollower, the I-V transforming circuit and the loop switch is conducted,and the I-V converting module enters into a sampling setup stage; andwherein when the loop switch is disconnected and the bypass circuit isenabled, the feedback loop is bypassed, and the I-V converting moduleenters into an I-V converting stage.
 2. The I-V converting moduleaccording to claim 1, wherein the I-V converting module furthercomprises a loop capacitor; and wherein the loop capacitor is connectedbetween the gate of the source follower and the input end of the I-Vtransforming circuit.
 3. The I-V converting module according to claim 1,wherein the bypass circuit comprises a bypass switch and a power supply,and the bypass switch is connected between the gate of the sourcefollower and the power supply; and wherein the bypass circuit isdisabled when the bypass switch is disconnected.
 4. The I-V convertingmodule according to claim 1, wherein the bypass circuit comprises afirst bypass switch, a second bypass switch, and a ground plane; whereinthe first bypass switch is connected between the gate of the sourcefollower and the ground plane; wherein the second bypass switch isconnected between the source and the drain of the source follower; andwherein the bypass circuit is disabled when both of the first bypassswitch and the second bypass switch are disconnected.
 5. The I-Vconverting module according to claim 1, wherein the I-V transformingcircuit comprises an inverting amplifier and at least one transformingpath; wherein the transforming path is connected between an input end ofthe inverting amplifier and an output end of the inverting amplifier;and wherein the input end of the inverting amplifier and the output endof the inverting amplifier form the input end and the output end of theI-V transforming circuit, respectively.
 6. The I-V converting moduleaccording to claim 5, wherein, the inverting amplifier comprises aninverter or an operational amplifier.
 7. The I-V converting moduleaccording to claim 5, wherein the transforming path comprises a resistorand a switch connected in series, or a capacitor and a switch connectedin series.
 8. The I-V converting module according to claim 1, whereinthe source follower comprises an N-type field-effect transistor or anNPN-type triode.
 9. The I-V converting module according to claim 1,wherein the loop switch is an electronic switch or a physical switch.